In recent years, a transmission bandwidth used for data communication is increasing steadily and increase of the speed and the capacity is advancing.
At present, for an interconnection where the transmission distance is several tens meters or more such as, for example, an interconnection between housings of servers, an optical link (data transmission using an optical fiber) which uses a wide transmission band and is less likely to undergo disturbance is utilized.
On the other hand, as the performance of an LSI such as, for example, a CPU, a memory (for example, a DRAM) and so forth increases and the processing speed increases, expansion of the transmission bandwidth in an information equipment such as, for example, a server has become required in order to implement an optical interconnection for carrying out high-speed signal transmission between LSIs.
Conventionally, in order to carry out high-speed large-capacity signal transmission (data transfer) between a CPU and a memory (here, a DRAM), for example, as shown in FIG. 15(A), a CPU 102 is mounted on a system board 100 (hereinafter referred to simply as board) of a server through a package board 101 and a plurality of memories 103 (here, DRAMs) are mounted in the proximity of the package board 101 on the board 100.
In this instance, as shown in FIG. 15(B) [schematic sectional view taken along line X-X′ of FIG. 15(A)], the CPU 102 and the DRAMs 103 are connected to each other by multi-layer electric wirings 104 formed in the board 100.
In such a configuration as just described, in order to drastically enlarge the transmission bandwidth between the CPU 102 and the memories 103, it is necessary to increase the transmission speed in a single wiring and increase the number of wirings.
It is to be noted that Patent Documents 1 to 7 specified hereinbelow were obtained as a result of a prior art search conducted regarding an optical interconnection or an optical modulator.
In Patent Document 1, a structure is disclosed wherein a reflection structure and a controlling electrode are provided at an end portion of an optical waveguide and an optical path is folded back in a small size and at low loss (refer, for example, to FIG. 2). In particular, an example wherein the structure is applied to a directional coupler is disclosed.
In Patent Document 2, an interface configuration is disclosed wherein, in order to carry out high-speed data transfer, an optical signal is produced from an electric signal by an optical modulator using an electro-optic effect (refer, for example, to FIG. 1).
In Patent Document 3, a configuration wherein an optical signal which propagates in an optical waveguide substrate is emitted to the outside of the substrate so as to be connected to an optical fiber (refer, for example, to FIG. 4) and a configuration wherein, in a multi-layer optical waveguide structure, refractive index variation (electro-optic effect) generated by voltage application is utilized to switch an optical signal between upper and lower layers are disclosed (refer, for example, to FIG. 13).
In Patent Document 4, a configuration is disclosed wherein, regarding a distortion measuring instrument which involves detection of a wavelength variation, a Bragg reflection type waveguide is used as a reflection structure in an optical circuit configuration which uses an optical waveguide (refer, for example, to FIG. 2).
In Patent Document 5, a configuration is disclosed wherein, as a photoelectric integration device, an LSI, an optical device, a driving circuit for controlling the optical device and wiring means (optical waveguide) to the optical device are accommodated in the same package (refer, for example, to FIG. 1).
In Patent Document 6, a configuration is disclosed wherein a reflection type optical modulator is used in a wavelength division multiplexing network (refer, for example, to FIG. 17).
In Patent Document 7, a waveguide type optical modulator (in particular, a Mach-Zehnder type optical modulator) for which an organic-based electro-optical material is used is disclosed (refer, for example, to FIG. 1).
Patent Document 1: Japanese Patent Laid-Open No. Hei 5-2116
Patent Document 2: Japanese Patent Laid-Open No. 2000-250671
Patent Document 3: Japanese Patent Laid-Open No. Hei 6-69490
Patent Document 4: Japanese Patent Laid-Open No. Hei 8-94328
Patent Document 5: Japanese Patent Laid-Open No. 2001-36197
Patent Document 6: Japanese Patent Laid-Open No. 2001-197006
Patent Document 7: Japanese Patent Laid-Open No. 2004-109457